Different types of auger are known in the prior art. As a general rule, the study of ground composition is made in the following manner. In a field, 10 samples are taken around a circle having a radius of 10 meters. Generally samples are taken at different depths depending upon the substances it is desired to detect. For example, to study the nitrate composition of soil, it is necessary to reach depths of approximately 90 cm. The study of nitrate composition is preferably made between October and March, at the time of year when the ground is wettest, and it is therefore easier to reach depths of 90 cm. For other soil components, the samples to be taken by the user may require lower depths, for example 30 or 60 cm.
A type of auger exists, formed of an elongated metal stem surmounted by a wheel intended to turn the stem so as to drive it downwards, which ends in a device in the shape of a gimlet intended to bore down to the desired depth and used to collect the sample at this depth by rotation. The problem with this auger lies in the fact that the same device, namely the gimlet, is used both for boring and for collecting the sample. It is therefore obvious that the soil cleared while the gimlet is driven downwards will be mixed with the soil taken at the desired depth.
In addition, if it is desired to take samples at different depths, the auger needs to be driven down to a first depth and then lifted back to the surface with the samples taken at this depth, and it is subsequently re-lowered down to a new depth, and again lifted back to the surface with the new sample taken at this second depth. This is a lengthy, tiresome process.
Finally, it often proves difficult to drive the auger down to 90 cm and to lift it back owing to the friction exerted on the gimlet and on the stem as the tool bores downwards.
Another type of auger is disclosed in document DE 3707589. This auger comprises a driving head formed of a tip fixed to the end of the stem. The head comprises a part offset towards the outside, the head section at this point being greater than the stem section. The section of the stem is of rectangular trapezoid shape. The stem is hollowed at regular distances over its length. The soil comes to be housed in the hollows along the stem subsequent to scraping achieved by rotation of the stem. During rotation, scraping is made by the projecting part formed along the length of the stem by the oblique side of the stem section. The part of the driving head that is offset is located perpendicularly above this projecting part so as to widen the hole and thereby provide some freedom of rotation to the projecting part in the widened part of the hole when the auger is driven down. Once rotation of the stem is initiated, the projecting part is no longer in the widened part of the hole and comes into contact with the earth on the side walls of the hole where the hole is not widened. When this type of auger is driven downwards, the stem undergoes ground friction and it becomes difficult to drive the auger down. This type of auger is made up of several parts and does not comprise any specific means to withstand the shock wave generated when it is driven down using a tool such as a hammer. In addition, this type of auger cannot be used to take samples over the entire depth.